Corrected optical system for shallow camera or the like,and components thereof



United States Patent Inventor James G. Baker Winchester, Mass.

Appl. No. 680,621

Filed Nov. 6, 1967 Patented Dec. 22, 1970 Assignee Polaroid CorporationCambridge, Mass. a corporation of Delaware CORRECTED OPTICAL SYSTEM FORSHALLOW CAMERA OR THE LIKE, AND COMPONENTS THEREOF Primary Examiner-JohnM. Horan Attorney-Brown and Mikulka and William D. Roberson ABSTRACT: Acorrected optical system is provided for a shallow camera that ischaracterized by an extremely short dimension between the forwardposition of the first refracting surface and the rearward position ofthe final image surface. In the compact handheld camera illustratedherein as an example, the optical system is panoramic in operation,comprising (at one end of the camera) a pivotal scanning mirror and (atthe other end of the camea) a slit, past which the photosensitive filmis moved at a linear rate, with which the scanning mirror rate issynchronized in order to synthesize a complete image from a continuoussequence of increments.

BACKGROUND AND SUMMARY OF DISCLOSURE The present invention relates tophotographic optics and, more particularly, to a corrected opticalsystem fora shallow camera that is characterized by an extremely shortdimension between the forward position of the first refracting surfaceand the rearward position of the final image surface. Such an opticalsystem isadapted for incorporation into a hand held camera, the heightand width of which are sufficiently large to accommodate a full sizephotographic frame that may be developed directly by diffusion transferor the like but the thickness of which is sufficiently small to permitthe camera to be carried unobtrusively in a clothing pocket .or thelike. Prior cameras having a like shallow front to back depth have beencharacterized by relatively small images because of the usuallyoccurring relationships between lens diameter and focal length. In onetype of camera incorporating a lens system of the present invention (seeU.S. Pat. application Ser. No. 549,961, filed May 31, 1966, in the nameof Edwin H. Land, now Pat. No. 3,405,619). the optical system ispanoramic in operation. In one form, such a camera comprises (at one endof the camera) a pivotal scanning mirror and (at the other end of thecamera) a slit, past which the photosensitive film is moved at a ratewith which the scanning mirror rate is synchronized in order tosynthesize a complete image from a continuous sequence of increments. Inthe design of such a compact system, it has beenfiound that severedifficulties are encountered in attempting to compensate for perspectivedistortions and to achieve good image quality by correction ofaberrations.

Primary objects of the "present'invention, for reasons that will beexplained in detail below, are: to provide a corrected optical systemthat is adapted in one form for application to panoramic scan operationin a hand held camera characterized by an X-direction along whichradiation from a field of view is received, a Y-direction with which aslit, that defines successive increments of a panoramic image, isparallel and a Z-direction with respect to which relative motion occursbetween the slit and a photographic film atthe image surface; to providean optical system of the foregoing type in which an objective lens arrayincludes a positive and a negative lens component (analogous to thefirst and second lens components of a Cooke triplet) for refractinglight from a scanning mirror in object space in such a way as tointroduce a substantially collimated flux into the remainder of thesystem; to provide an optical system of the foregoing type containing atleast 5 a pair of opposed prisms which pivot in synchronism and in afunctional relationship with the relative motion between the slit andthe photographic film to compensate for variations in off axismagnification resulting perspectively from operation of the scanningmirror; to provide a Schmidt type lens array with residual aberrationsthat are substantially opposite those of the objective lens array so asto combine with the objective lens array to produce excellent correctionfor various chromatic and seidel aberrations; and to provide adjacent tothe photographic image surface a zoom lens array with low net power thatpermits variation in the focal length of the system by virtue ofrelatively movable high power components which provide appreciablesensitivity to spatial variation without destroying image quality andwithout movement of the critically positioned forward refracting surfaceand photographic image surface. Although the foregoing components areshown herein as being useful in a panoramic hand held camera, it is tobe understood that certain of the specific relationships are useful inother arrangements where similar problems of aberration correction areencountered.

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

The invention accordingly comprises the apparatus possessing theconstruction, combination of elements and ardetailed disclosure, thescope of which will be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THEILLUSTRATED EMBODIMENT Generally, the camera of FIG. 1 comprises ahousing 20, shown in phantom lines, that encloses and supports theoptical and photographic components. The photographic components forexample include a photosensitive stratum 22 and animage receptivestratum 24, the former being constituted for advancement relative to theoptical system in a manner to be described below and the latter beingconstituted for superposition with the latter in the presence of aninterposed processing fluid 26, by operation of a pair of pressurerollers 28, 30. The resulting sandwich is ejected through a slot 32 atan extremity of the camera and the resulting picture may be strippedfrom the sandwich thereafter. Details of the composiprinciples of the'tions of photosensitive stratum 22, image receptive stratum 24 andprocessing fluid 26 are described in U.S. Pat. No. 2,543,181, issued onFeb. 27, 1951 in the name of Edwin H. Land. It will be understood thatother configurations of photosensitive and receiving strata arecontemplated, one such configuration specifically including thephotosensitive and receiving strata in an integrated sheet.

The parts of the illustrated optical system now will be describedbriefly to provide preliminary comprehension of overall function andoperation, as a basisfor the detailed explanation to follow. As shown inFIG. 1, this system comprises: a window 40 which communicates theoptical system with the objective view along an X-direction 41;'ascanning mirror 42, which varies the attitude of the optical systemwith respect to the field of view while deflecting the optical pathalong a Y- direction 43; an objective lens array, including a positivelens the motion of scanning mirror 42 to compensate for variations inoff axis magnification from operation of the scanning mirror; atrapezoidal, plane mirror (or alternatively a totally internallyreflecting prism) 52 for deflecting the optical path along a Z-direction53; a cemented doublet 54, 56 constituting part of a Schmidt type lensarray, in association with an aspheric surface at the rear of prism 50,(or alternatively at the front of prism 48), having residual aberrationsthat are substantially opposite those of objective lens array 44, 46 soas to combine with the objective lens array to produce excellentcorrection for various chromatic and seidel aberrations; a zoom lensarray having a negative lens 58 and a positive lens 60, the refractingsurfaces of which are disposed in proximity with a slit 38 along theY-direction substantially throughout the width of the camera but arerestricted in the direction of the X-direction and an elongated planemirror 62 for deflecting the optical path along the X-direction to theimage surface and the photosensitive stratum therein. In operation, asuitable drive 64, 66, 70 rotates scanning mirror 42, oppositely pivotsprisms 48, 50 and rotates pressure rollers 28, 30 in order to advancephotosensitive stratum 22 past slit 38 and rangement in parts, which areexemplified in the following spreads processing fluid 26 betweenphotosensitive stratum 22 and print receptive stratum 24 as the sandwichformed thereby emerges from a lighttight slot 32 in housing 20. Asshown, drive 64, 66, 70 includes three mechanically isolated, miniaturetorque motors, that are powered by a dry cell 74 under the control of asolid state circuit 76. Following a development period, conventionallyranging between seconds and aminute, the photosensitive and imagereceptive strata are stripped apart to reveal the regular-sizephotographic 'print. The forward focal distance is variable by simplyadjusting manual knob 68 which controls the positions of negative lens46, cemented doublet 5d, 56 and zoom lens elements 58, 60. The mountingswhich establish these positions are connected by a suitable linkage (notshown). A shutter (not shown) at window 40, in one form, assists scanmirror 42 in excluding undesired light from within the camera housingand a closure (not shown) at the back of the camera housing enablesreloading thereof conveniently.

The structure and function of the components of the lens system now willbe described in detail.

Objective Lens Group 44, 46 and Correcting Prisms 43, 50

Although the depth of the illustrated camera from forward refractingsurface to rearward focal plane is unusually shallow, the lens systemaxially is unusually long for its focal length. The manner in which thisunusual length is achieved will be described below. The reasons for thisunusual length are the specified depth of the housing as being less thanone inch, the specified position of the entrance window as being locatedat the upper left hand corner as the user sees it from behind, thespecified use of transfer diffusion photographic materials, thespecified choice of a fixed image size and position which, for infiniteobject distance, corresponds to an approximately 5- inch focal length(for a wide range of object distances), the space needed for diagonalsweep mirror 42, the space needed for trapezoidal mirror 52, the spaceneeded for elongated mirror 62 and the specified slit position.

A panoramic camera of the type disclosed introduces a number of problemsnot ordinarily encountered in snapshot I photography. For example, inthe present case, photosensitive stratum 22 is to be moved at a constantrate past slit 38 while lying in a plane at right angles substantiallywith respect to original X-direction 41.. Ordinarily, a flat field lenssystem produces an image on a photosensitive stratum at the focal plane.However, in the present case, when the field of view is scanned by suchmeans as diagonal sweep mirror 42, in the meridional plane, the imagerate is exactly that of the photosensitive stratum rate only at thecenter of the slit. With a reasonably narrow slit width, in the presentcase a maximum of 0.4 inches, there is a slight but acceptable blurringwhich is caused by the slight difference between the positions of pointsalong an arcuate cylindrical surface defined by the scan mirror aboutits axis and the corresponding positions of points along a plane thatwould be defined by the operation of the lens I system itself. Along thelength of slit, it obviously is necessary that the optical designproduce a flat image in the Z-direction and that the distortion over thefull length of the slit be held to say: 1 percent of the mean valueadopted for the entire panoramic image. To this extent, the opticaldesign for this panoramic camera becomes similar to that of a snapshotcamera. However, a snapshot camera would require a wider field inasmuchas the diagonal of a square image, for example, would be 1.4 times thelengthor width of the image. The optical design of the contemplatedpanoramic camera need only cover the width of the image since thelength-is generated by the scanning operation, and no diagonal dimensionis encompassed by the optical system. The optical system is shown inFlG. 2 as being unfolded along a single axis for ease of explanation.

As shown in FIG. 2, the objective lens array includes window d0,scanning mirror 42, positive lens element 44 and negative lens elementas. By design, for an adopted mean object distance of 25 focal lengths,the rays emerging from negapositioned at positions along theaxisotherthan the positions shown withoutchange in princip of operation.

Prisms 48, 50 are provided iri'i'e'sponse to the fact that a panoramiccamera causes the image to contain a distorted perspective for normalpurposes, namely, that which a pinhole camera wouldproduce on a strip offilm lying on a right circular cylindrical surface centered atthepinhole. As shown in FIG. 3', in a panoramic camera, a gridor reseau inobject space projects into a planar array where the previously straighthorizontal lines become curved as at toward the meridional plane of thescanned picture from above and below, the amount of the curvaturedepending on the cosine of the offaxis angle. The vertical grid lines inobject space remain vertical as at 82 but are compressed on either sideof the axis toward a central line by an amount depending on the cosinesquare of the field angle, insofar as the magnification locally isconcerned, butby a displacement proportional to the difference ofthetang'ent and the arc of the angle insofar as the actual absolutedisplacement is concerned. The. present optical system is intended tocornpensate-for this cylindrical projectionlerror by mearis both ofa"zoom"action depending on the offaxis angle, as will be describedbelow, and by a pivoting of prisms 48, 50. Prisms 48, 50 are introducedhere in order to obtain a variable angular magnification in themeridional plane of the lens system. Parallel light refracted throughsuch a prism pair at so-called minimum deviation, where each of theprisms refracts in an opposite sense with respect to the other, emergesaccurately parallel and with unchanged magprism equally and oppositelyso that the emergent light will remain parallel but so that the angularsubtense of any distant object viewed through the prism pair will bealtered by a calculable amount. It is essential that the prisms bearranged to produce equal and opposite refractions in order that nolateral color dispersion be introduced into the emergent beam. That is,entering white light must emerge as white light, undispersed.

Prism pair 48, 50 is at minimum deviation at the center of the scan,that is, for the centerstrip of the panoramic picture.

Off center, progressively, the prism pair produces in an angular sense arequisite change in magnification that combines with the followingcomponents of the optical system to yield a magnified image at slit 38which by design becomes a single cosine correction factor in themeridional plane of the scan.

Thus, the cosine squareerror is reduced to a single cosine error tomatch the remaining single cosine error in the direction perpendicularto the direction of movement of the photosensitive stratum.

Prisms d8, 50 must operate in parallel or nearly parallel light in ordernot to intr oduce additional astigmatism' into the optical image at thebeginning or end of the scan. At minimum deviation for the center of thefield, there is no appreciable astigmatism and would be none even if thelight were not parallel. The prisms pivot about axes 82, 34 by equal andopposite amounts from their positions at the center of the fieldmidpoint of the scan action) where they are at minimum deviation.

It should be noted that in such a prism pair arrangement,

full symmetry necessarily is lacking. The reason for the slightassymetry is that, although the required image enlargement both at thebeginning and end of the scan is achievable as described, the followingfactors contribute to the final effect. It is true that the prism pairat the beginning and at the end of the scan occupy positions analogouslyaway from the minimum deviation. However, the rate of change, acrossincrements (as determined by the width of slit 38) of the field beingscanned, is increased at the initial or final increments of the imageand is decreased at oppositely located increments of the image dependingon which of the two relative pivotal relationships for pair of prisms48, 50 is selected. For a narrow slit of the type herein contemplated,say 0.4 inch in maximum width, the problem is well within acceptablelimits. For a wide slit, there might be no additional blurring actionone side of center but a double blurring action on the other side. Inone alternative form of the invention, such blurring with a relativelywide slit is eliminated by a second prism pair, the motions of which areopposite corresponding motions of the first prism pair. Also, inalternative forms of the optical system, prisms 48, 50 are moved eitherto a position immediately preceding positive lens 44 or to a positionimmediately preceding sweep mirror 42, without change in function. Inanother alternative form of the present embodiment, objective lens array44, 46 is pivoted about a point on the optical axis appropriatelybetween lens 44 and lens 46 to obtain additional outward distortionofi-axis as a function of scan angle in order further to compensate thecylindrical projection aberrations.

Schmidt Lens Array 54, 56 and Asperic Surface R With reference now toSchmidt type lens array 54, 56, it will be recalled that the so-calledSchmidt optical system employs two principles. The first is that ofsymmetry of reflecting or refracting surfaces about a center ofcurvature. The second is that of positioning a correcting surface at thecenter of curvature to remove spherical aberration over a wide field ofview. In the present Schmidt arrangement, the indices of refraction ofcemented elements 54, 56 are either identical at a mean wave length orso nearly so that residual aberrations are acceptable for thephotography to be achieved. The initial surface of lens 54 is taken tobe plano or sufficiently so that the residual aberrations areacceptable. Under these conditions, the center of curvature of the rearsurface of lens 56 is taken to lie by refraction at the rear vertex ofprism 50. If one were to put an artificial star point as a source oflight at this rear vertex 86, the rays after refraction through lenses54, 56in a mean wavelength, would emerge as radii of the rear sphericalsurface of lens 56. To complete the Schmidt lens arrangement, the rearsurface of prism 50 is aspheric in such a way as to produce a sharplyfocused axial image at-the final image plane of the system for the fullfl8 beam. Even though prism 50 rotates about axis 84 which is throughvertex 86, the aspheric is so weak optically that no harmful aberrationsare introduced into the final image. As indicated above, in analternative embodiment the aspheric surface and the center of curvatureare at the front face of prism 48. In another alternative embodiment,prisms 48, 50 are replaced by a substantially plane parallel element,one or both of the surfaces of which are aspheric.

Schmidt type lens array 54, 56, together with its associated asphericsurface at 86, comprise a well corrected optical system except for somecurvature of field, a large inward or barrel distortion and some coloraberration. Similarly, objective lens array 44, 46 is an equally wellcorrected optical system but with opposite curvature of field, anoutward or pincushion distortion and opposite color aberration. The twoarrays in tandem thus produce a fiat image with acceptably small netdistortion and with entirely adequate color correction includinglongitudinal, lateral and chromatic variations of the seidelaberrations. It will be noted from the drawing that the optical systemis physically quite long for its focal length. In one form of theillustrated embodiment, as shown, the overall length from the frontsurface of lens 44 to the final image plane is 6.487 inches, whereas thefocal length is 5 inches. Some of the physical length of the illustratedsystem has been obtained by use of the Schmidt array, inasmuch as aSchmidt system is quite long for its focal length even as a separatesystem.

Specific Example Illustrating Combination of Objective Lens Array 44,46, and Schmidt Lens Array 54, 56

The specific example of the following table lists representativenumerical values for the radii, thicknesses, indices of refraction andAbbe numbers of an optical system of the foregoing type, includinglenses 44, 46, prisms 48, 50 and lenses 54, 56. Elements 58, 60, whichare not necessary to the optical system of the following specificexample, will be described later. As indicated above, in the followingsystem, the focal length 5 inches, the side-to-side field angle 38 andthe speed is fl8.

When two optical systems that are separately corrected are placed intandem, additional degrees of freedom for the alignment are introduced,particularly if the intervening axial bundle is of parallel light, ashere. The first system can be displaced along the axis, or rotated, ordisplaced laterally. It will be recalled that as the stages of opticaldesign proceed toward a more highly corrected image, the optical systembecomes increasingly less dependent on the choice of the position of theentrance pupil (and therefore of the exit pupil). In the limit if theentering light is parallel and the emergent light is not only strictlyparallel but has angular magnification (as in a telescope), the positionof the pupil becomes relatively unimportant. In the case of two suchsystems in tandem, the exit pupil of the first can be regarded as theentrance pupil of the second. If neither is sensitive to the position ofthe pupil, it follows that the positioning of the first optical systemrelative to that of the second allows some freedom. in the system athand, the separate field and Schmidt groups actually are not fullycorrected but they are sufficiently well corrected to allow some freedomof relative movement. For example, objective lens group 44, 46 iscorrected for spherical aberration, coma and astigmatism for a rearstop, but do have a strongly negative (overcorreeted) curvature offield. Schmidt group 54, 56, R, also is free of spherical aberration,comma and astigmatism but has strongly positive (undercorrected)curvature of field. The off-axis wave fronts therefore are divergent andconvergent in the two systems but otherwise are stigmaticallycorr'ected. Matching these curvatures of the wave fronts results in anet flat field for the overall system, notwithstanding relative movementof the systems laterally or longitudinally. In one modification of theillustrated embodiment, this freedom allows the option of using zoomaction to obtain focus and any reasonable variation desired in focallength.

It should be noted that in the illustrated optical system, longitudinaland lateral color aberration have been eliminated much as it isaccomplished in the case of the ordinary triplet. Because of the largeair spaces, however, and because of the need to minimize the residualcolor aberrations, while adjusting for required location the Schmidtcomponent has incorporated a cemented doublet instead of a singleelement.

Zooming Without Zoom Lens Array 60, 62

In the illustrated optical system, if zoom lens array 60, 62 is notconsidered, there are four air spaces d d d and d lnasmuch as prism pair48, 50 has no appreciable optical power, d and d do much the same thingand can be regarded as a single parameter. Moreover, it will be recalledthat the center of curvature of the Schmidt group is at 86, a conditionwhich exists only if d is held fixed. Nevertheless, in an alternativeform of the illustrated embodiment, longitudinal motions in d of i 0.5inches can be tolerated when it is desirable to move only the cementeddoublet and to omit prism pair 48, 50. The three effective parameters,namely d d d and d under these circumstances, allow compensation forfocal position, focal length and some third order aberrations in orderto offset changes caused either by focusing for different objectdistances or for zooming the focal length to obtain the requiredcorrection for the remaining single cosine factor in Y and Z direction,or both. Although, in various modifications of the illustratedembodiment, synchronized movements involving these three parameters arecontemplated for zooming focal length in one form and for aberrationcompensation in another form, as is to be expected with only 3 freeparameters, the aberrations become significant outside a rather narrowrange of focus.

An additional desired feature is that the sweep action of the scanmirror should be the same regardless of object distance. In other words,where mechanical simplicity is paramount, it is desired that only asingle mechanical or electromechanical movement be utilized for the scanaction and that the focusing for different object distances beaccomplished separately. This of local magnification in the relatedcylindrical projection along the Y and Z directions. (Prism pair 48, 50compensates for the additional cosine factor in the Z-direction). Thissingle cosine factor isobtained by a calculated change in the scale" atthe particular off axis angle of the instant. This change in scale mustbe accompanied by holding the focus at image plane 61. The 2 freeparameters above discussed then may be determined by solving thenecessary equations by iteration. Since the relationships also are afunction of object distance, a double entry of spacings versus objectdistance, where image size and position are held independent of objectdistance.

In the following table, the lens system has, at null position, a 5-inchtable focal length and an object distance of focal lengths( 10 feet 5inches). In one form, the total picture scan time is one-third second.

TABLE II 1./s. (Reciprocal Object Distance) Spacing .00 .01 .02 04 08 1632 Adz 0310 0251 -.0191 .0068 0198 0882 .1710 [M14 0310 0251 0191 .00680198 0882 .1710 Add 1985 1718 .1441 .0854 0510 5002 .6580 Ad, 1985 .17181441 .0854 .0510 .5002 .6580

Adz -.0444 .0390 .0336 -.0225 0006 0522 .1685 Ad! .0444 0390 0336 .0225-.0006 .0522 .1685 Ado 3765 3549 3330 -.2875 .1887 0588 6531 Ads 3765.3549 3330 .2875 1887 0588 .6531

The tabulation shows that the movement of lens element 46 iscomparatively small, a consequence of the strong optical powers of firstand second lens element 44, 46. The longitudinal movement of Schmidtgroup 54, 56 is quite large, amounting to more than half an inch at thebeginning and end requires that the image size and position, both as afunction of of the Picture scan at the mean focal distance, and to morescan and as a function of object distance, remain the same by zooming ofthe air spaces for any usable object distance. For a pure zoom systemutilizing only longitudinal movements of the components, only the airspaces are available as parameters and indeed only through ranges thatare permitted by the mechanical details of the camera and bynoninterference of one element with another. In the panoramic systemunder consideration, the air space between sweep mirror 42 and forwardvertex 88 of lens element 44 is held constant to prevent contact withmirror 42. In the illustrated system, as mentioned earlier,the only freeparameters are d d, d and d If vertex 88 is to remain fixed, then lenselement 44 is fixed. Therefore, only lens element 46 moves, inasmuch asprism pair 48, 50 must not move longitudinally. As a consequence, theincremerit of movement in space d is always the negative of thecorresponding increment of movement in space d Similarly, if Schmidtlens group 54, 56 moves, the associated increment of movement in space dis equal to the negative of the corresponding increment of movement inspace d Thus there ac tually are only two free parameters when theoverall length is held fixed and only two components are moved. In amodification of the illustrated embodiment that omits zoom lens array58, 60, these two free parameters are adjustable in such a way thanthree-fourths inch, for the on-axis requirement at an object distance of15-% inches. Since most hand cameras focus only to about 3 feet for a 5inches focal length, the achieved result here is unusual. The movementis executed twice during the scan, the center being the mean position.For the object distance of 25 focal lengths, the displacement of Schmidtgroup 54, 56 averages 0.5373 in one-third second or 1.6 inches/second.The actual movement is nonlinear, however, and is of a quadratic natureresulting from the first variable term in the expansion of the cosine.

Zoom Lens Array 60, 62

It is obvious that in the embodiment above described, with only two freeparameters, most versatile control cannot be exercised over thevariations in the aberrations such as longitudinal and lateral color,spherical aberration, coma, astigmatism and distortion. (Many zoomsystems employ achromatized components to minimize the variations incolor correction with zooming. In this respect, any variation in lateralcolor usually is more serious than the one in longitudinal color and canpreclude acceptable wide angle performance). In the illustratedembodiment, in order to obtain additional free parameters, zoom lensarray 58, 60 has been introduced. Noras to hold image size and positionat desired values for any mally, one would design a system of this typeto make. maxreasonable object plane distance and for magnificationchanges needed during the sweep to produce the necessary zooming andperspective changes in the photograph.

It will be recalled that during the sweep action of mirror 42, a singlecosine factor must be obtained to compensate for loss imum use of allthe new parameters (four radii of curvature, two thicknesses, onecentral air space if not cemented, possible aspheric surfaces, twoindices'of refraction and two vvalues.) In the present embodiment,however, it is desired to achieve a wide zooming range without upsettingpreviously described performance. Zoom lens array 58, 60 is such thatits external surfaces 62, 64 are substantially piano. Outer surfaces 54,56 are either piano or have like large radii of curvature so that theyhave small net coma and astigmatism and possibly some sphericalaberration and curvature of field. inner surfaces 59, 61, which aresubstantially identical, are lrtrge enough to encompass the maximumdimension of the image. The longitudinal color that is generated by zoomlens group 58, 60 is slightly overcorrected but tolerable at f/ 8/0. inan alternative embodiment, the negative and positive zoom lenses arepositioned more closely to the Schmidt lens array, with outer surfacesof the zoom lenses constituting a shell having a radial centersubstantially concentric with the Schmidt lens surface and innersurfaces that are substantially aplanatic.

in one form, lenses S8, 60 are composed of lanthanum crown glass havingan index of refraction of L691 and a vvalue of 54.7. The high v-vaiueminimizes the color aberration introduced into the system. The highindex of refraction, which need not fall within critical tolerances, fora given total thickness of lenses 58, 60 taken together, provides greatoptical power in a small physical space and in turn minimizes mechanicalmovement in the zoom operation.

The following radii and thicknesses of lenses 58, 60 are typical.

TABLE III Lens or Thickness and airspace Radius spacing Rm=plan 53 d=0.125 -h0.010

Rr1=+ Airspace... d1r=.3250=e variable R12=+3.333 50 d 9=0.650:l:0.010

Rr1=plano in the illustrated embodiment, lenses 58, 60 are movable.Thus, the movable lens elements are lens 46, cemented doublet 54, 56 andlenses 58, 60, the variable air spaces 1 thereby being d,, d d 11,, dand d As was indicated before the increment in (1, remains the negativeof the increment in d,, the increment in d affects the increment in d,and the increment in d, affects the increment 11,.

In the following table, for a 0.04 reciprocal object distance, lenselement 58 remains essentially at null. Like the optical system of table11, the system has an approximately inch focal length and an objectdistance of 25 focal lengths (10 feet 5 inches) at null position. in oneform the total picture scan time is two-thirds second.

TABLE IV 1./s. (Reciprocal Object Distance) Spacing .00 .01 .02 .04 .08.16 .32

-.0093 -.0001 .0004 .0139 .0431 1133 .0093 .0001 -.0004 -.0139 .04311133 .0000 -.0022 -.0072 -.0142 -.0125 0334 -.0374 -.0270 .0033 .0273.0312 0320 Adtr.. .0913 0773 .0027 .0334 -.0250 420 -.3522 Mun"...-.0470 -.0405 -.0330 -.0179 .0124 .0733 1302 ad: -.0090 -.0000 -.0031.0029 .0150 .0409 1027 M1. .0090 .0000 .0031 -.0029 -.0150 -.0400 -.1027-.0413 -.0400 -.0s00 .0599 -.07s0 -.1054 -.0374 -.1152 -.1039 -.0920-.0097 -.0239 .0010 .1474

Adr:.-....- -.1839 1707 -.1003 -.1544 -.1237 -.0025 .0574

*The reciprocal object distance 0.04 has been taken as the mean valueand the table above gives the displacements in inches from the nullspacings for 0.0-1 on-axis.

In taking advantage of the possibilities introduced by the additionalfree parameters afforded by zoom lens elements 58, 60, improvedperformance is permitted by requiring a minimization of the sum of thesquares of the weighted changes in the aberrational coefficients oflongitudinal color, lateral color, spherical aberration, coma andastigmatism. The iterative solution thus cannot be compared directlywith that of table II, it being expected that the air space changesgenerally will be smaller in every case. However, a comparison of tablesII andlV with respect to magnitude of air space changes makes itapparent that for object distances including and greater than 25 focallengths, only modest changes of air space occur in table IV even atclose object distances.

in the illustrated system, if inner surfaces 59, 61 were truly aplanaticin the case where zoom lenses 58, 60 are as close to the image plane asshown, they would be too curved to admit the required field of view inthe Z-direction. However, as zoom lenses 58, 60 are moved closer to theimage plane, the relative height of the paraxial on-axis ray becomesrapidly smaller. This means that spherical aberration, coma andastigmatism become smaller and smaller anyway, regardless of whetherinner surfaces 59, 61 remain aplanatic or not. It should be realizedthat spherical aberration, coma and astigmatism a plano-plano opticalplate in the rear image space are independent of the position of theplate in this rear image space. That is to say, if one introduces athick plate into the rear air space of an already designed opticalsystem, the three aberrations then introduced as a consequence of thethickness of the plate have the same computed values regardless of thelocation. In view of the foregoing, zoom lenses 58, 60 are designed withouter surfaces 59, 61 piano because the associated minor aberrations canbe tolerated and with inner surfaces 63, 64 arbitrarily and analogouslynegative and positive respectively to approach at least to some extentthe aplanatic condition. As shown, the common radius of inner surfaces63, 65 is such as to permit about a half-inch variation in thickness ofeither element, with a small uncemented central air space there between.

TABLE V The null spacings are:

d 0 1656 d, 1000 d 1 5000 d 2 7369 d 3250 d 6322 The four decimals aregiven to prevent approximation errors but tolerances are quite normal.The overall length from the front surface of lens element 44 to theimage plane is fixed at 6.940 inches throughout the movement. The scalein the image plane is so adjusted that the sweep action is the sameregardless of the object distance although the sweep rate varies acrossthe field, always in the same way. For zero air space air space the pairconstitute merely a thick plate interpolated into the beam. However, thenull air space has been taken as 0.3250 inches to allow for plus andminus variations. The focus now extends from infinity to the 0.16 columnin table IV without encountering negative air space CONCLUSION changesmay be made in the above disclosure without departing from the scope ofthe present invention, it is intended that all matter shown in theaccompanying drawing and described in the foregoing specification beinterpreted in an illustrative sense.

lclaim:

1. A handheld shallow camera having a depth that permits it to bereadily carried in a clothing pocket and a width and length that permitsthe generation therein of an image of snapshot size for development bytransfer diffusion, said camera being characterized by an X-directionalong which radiation from a field of view is received, a Y-directionalong which is oriented a slit that defines successive increments of apanoramic image and a Z-direction along which relative motion occursbetween the slit and a photosensitive stratum at the image surface, saidcamera comprising a scanning mirror for varying the attitude of theremainder of the optical system with respect to the field of view, anobjective lens array including positive lens means and a negative lensmeans for refracting light from said scann ng mirror in such a way as tointroduce a substantially collimated flux into the remainder of saidoptical system, at least a pair of opposed prisms which pivot insynchronism with said relative motion between said slit and saidphotosensitive stratum in order to compensate for variations in off axismagnification, a Schmidt type lens array with residual aberrations thatare substantially opposite those of said objective lens array so as tocombine with said objective lens array to produce correction for variouschromatic and seidel aberrations and a zoom lens array contiguous withsaid image surface, said zoom lens array including forward negative lensmeans and rearward positive means, said movement of said scanningmirror, said movement of said opposed prisms and said relative movementbetween said slit and said photosensitive stratum being synchronized tophotoexpose said photosensitive stratum to said panoramic image.

2. The camera of claim 1 wherein at least one surface of said opposedprisms is substantially perpendicular to said Y-axis and is an aspheric.

3. The camera of claim 2 wherein the center of curvature of the finalsurface of said Schmidt type lens array is taken to lie by refraction atthe vertex of said aspheric.

4. The camera of claim 1 wherein said negative lens means and saidpositive lens means of said Schmidt type lens array constitute apartially achromatized pair.

5. The camera of claim 1 wherein means are provided to move saidnegative lens means of said objective lens array, said lens means ofsaid Schmidt type lens array and at least one of the lens means of saidzoom lens array in synchronism to adjust image size and position.

6. The camera of claim 1 wherein said objective lens array and saidSchmidt type lens array are characterized by substantially equal andopposite curvatures of field.

7. The camera of claim 1 wherein the lenses of said zoom lens array arecharacterized by opposed outer surfaces that are substantially plano andadjacent inner surfaces that are analogously divergent and convergent.

8. The camera of claim 1 wherein the internal surfaces of said zoom lensarray are of relatively strong power, individually and of relatively lowpower combined.

9. A handheld shallow camera having depth that permits it to be readilycarried in a clothing pocket and a width and length that permits thegeneration therein of an image of snapshot size for development bytransfer diffusion, said camera being characterized by an X-directiortalong which radratlon from a field of view 18 rece ved, a Y-drrecttonalong which is oriented a slit that defines successive increments of apanoramic image and a Z-direction along which relative motion occursbetween the slit and a photosensitive stratum at the image surface, saidcamera comprising a scanning mirror for varying the attitude of theremainder of the optical system with respect to the field of view, anobjective lens array including a positive lens component and a negativelens component for refracting light from said scanning mirror in such away as to introduce a substantially collimated flux intothe remainder ofsaid optical system, at least a pair of opposed prisms which pivot insynchronism with said relative motion between said slit and saidphotosensitive stratum in order to compensate for variations in off axismagnification, a Schmidt type lens array with residual aberrations thatare substantially opposite those of said objective lens array so as tocombine with the objective lens array to produce correction for variouschromatic and seidel aberrations, and a zoom lens array including aforward negative lens component and a rearward positive lens component,one surface of said opposed prisms being substantially perpendicular tosaid Y-direction and being an aspheric, the center of curvature of thefinal surface of said Schmidt type lens array being taken to lie at thevertex of said aspheric, said negative lens of said objective lensarray, said Schmidt type lens array and at least one of the lenscomponents of said zoom lens array being movable in synchronism, wherebysaid movement of scanning mirror, said movement of said opposed prismsand said relative movement between said slit and said photosensitivestratum are synchronized to photoexpose said photosensitive stratum tosaid panoramic image.

10. The camera of claim wherein the remote refracting surfaces of saidzoom lens array have relatively weak power and the contiguous refractingsurfaces of said zoom lens array have relatively strong power.

11. The camera of claim 9 wherein the contiguous surfaces of said zoomlens array are substantially aplanatic.

12. The camera of claim 9 wherein movement of the components of saidzoom lens array causes change of focal position.

13. The camera of claim 9 wherein movement of the components of saidzoom lens array causes change of image size in a given image surface.

